168: The Battle for Oslofjord


The German ships on their way to Oslo were in for a nasty surprise, courtesy of the Norwegian defenders of the fortress at Oscarsborg.



Hello everyone and welcome to History of the Second World War Episode 168 - The Invasion of Norway Part 6 - The Battle for Oslofjord. This week a big thank you goes out to Anthony and Ronnie for choosing to support the podcast by becoming a member, you can find out more about becoming a member over at historyofthesecondworldwar.com/members. Each of the areas that the Germans targeted in their invasion were important for their own reasons, but it would be hard to argue that the most important target for the German landings was the Norwegian capital of Oslo. The goal of the invasion was to quickly bring the Norwegian’s to the negotiating table to allow for some kind of agreement to be made which would prevent the German Army from getting pulled into a long and costly campaign of conquest. The best way to do this was to take over the political center of the country, and begin negotiations with either a captured government or at least one that was on the run from German troops. Of course the Norwegian government and military understood the importance of Oslo, it was the capital of their nation after all, and so there were defenses in place to prevent a seaborne invasion from taking place. These defenses, and the determination of the men who manned them, would surprise the Germans, resulting in even more drastic consequences than the staunch defense of Kristiansand which had damaged the Admiral Hipper.

The approaches to Oslo fell under the 1st Sea Defense District, with the District stretching from the Swedish border all the way to Egersund in western Norway. They would receive information on April 8th that German ships had been spotted moving through Danish territorial waters, which meant they could be headed to Norway. Just before 4PM in the afternoon the commander of the district was informed that the British were moving out to try and intercept the German ships, and then a few hours later orders were given to bring the defenses around Oslo to a higher state of alert. At around 11:30 the primary forts reported that they were as ready as they could be, with both their searchlights and their guns manned and ready to use. The smaller searchlights would prove to be mostly useless due to fog, but the larger searchlights would be useful. Just a few minutes after the forts reported ready two ships were spotted moving up the fjord towards them. These were the ships of the German task force assigned to the Oslo operation, and they were led by the German cruiser Blucher. The commander of the Blucher, Kummetz, wanted to pass the forts at around 3:30 in the morning, but that meant that they actually had to enter Norwegian waters well before that, which is when they were spotted. The German ships would slowly move up the fjord, at a speed of only ten knots, which gave the men on board plenty of time to build up their stress. They were not helped by the fact that it was foggy and there was some growing morning light, the combination of which made it very challenging to see much of anything on shore. The first shots to be fired would be from the Rauøy fortress on the outer edges of the Oslofjord. The fort and the German ships ended up shining searchlights at one another which made any spotting very challenging, but after two warning shots were fired by the Norwegian guns, and the ships still did not stop, the following shots were fired at the ship. While the shots were observed by the Germans, none would actually hit the German vessels. This encountered was reported to Norwegian high command, as would other sightings of the German ships as they continued on their way, they still had about 75 kilometers to go before reaching Oslo. Roughly two thirds of the way from Rauøy to Oslo was another Norwegian fort, Oscarsborg which was critical to the defense of the capital due to its position at one of the narrowest areas of the fjord, perfectly positioning the fort to interdict any enemy movement. The main guns at Oscarsborg were 3 28cm Krupp guns that were in open, but shielded, batteries on an island in the middle of the fjord, these were joined by three 15cm guns on the mainland and then 6 smaller guns at other areas. There were also some fixed torpedo tubes that could be used to fire into the channel in and underground torpedo battery which was completely unknown to the Germans. The battery was old, having been a part of the original construction back in 1900, and the 9 torpedoes that it could fire were of similar vintage, but they would prove that sometimes age doesn’t matter. The final piece of the fortifications that could have been used was the ability to lay a minefield across the channel to prevent any ships from transiting past the fort, but these took time to lay down and by the time that the orders to prepare the fort for action arrived there was no longer time to deploy the mines. This lack of time also made it difficult to get the guns manned and prepared, with the biggest problem being the biggest guns, the 28cm guns. On the evening of the 8th the defenses at Oscarsborg were at only about 1/3 of their full strength, and the 24 trained men and 4 officers could only effectively man two of these guns because each one of them took 11 men to load and fire. The commander of the fort, Oberst Eriksen, decided that two of the guns would be manned, and then he would use the 70 non-combatant personnel that were present to move ammunition to the guns. The torpedo battery would also be manned with enough men to fire the torpedoes. The manpower situation on the mainland was a bit better, but many of the men in those forts were quite raw and had only arrived a few weeks before for training.

As the Germans approached Oscarsborg the heavy cruiser Blucher was in the lead, and when they were first spotted Eriksen inside of the fort had a decision to make. Beyond the notification that had been received hours earlier that German ships were moving up the fjord, he had received no further instructions from the government or his commanding officer. No information about the invasion had reached him, and as far as he was concerned Norway was still a neutral country, which put a lot of weight on his shoulders. If this was not a German invasion force he might be bring Norway into the war by firing, if he did not fire he was allowing ships to just wander past his guns while doing nothing, and if they were executing an invasion he would have opened the door for them. Just before 4AM he would make up his mind to engage the ships, sending orders to the torpedo battery that they should open fire on the ships when presented with the opportunity. The firing would begin at around 4:20AM. In April at the latitude of Oscarsborg dawn was breaking as the first shots were fired from Oscarborg, with the range to be Blucher being just 1800 meters which was basically nothing. The very first shell would hit Blucher’s superstructure just below the bridge, and the second would hit the side of the ship, destroying a secondary gun mount and killing the army soldiers that were gathered in the decks below. Onboard Blucher orders were given to return fire, but it was very difficult to see anything ashore and so it was hard to know what to even shoot at. Things were also about to get worse for Blucher because as soon as Oscarsborg opened fire, so did several of the mainland forts in the area, with their commanders no loner hesitant to fire at the ships. These shore batteries only have 15cm guns, but they were able to pump a lot of shells into the Blucher very rapidly. The biggest problem that the Blucher had was that even these small shells were able to easily penetrate and damage the ship’s superstructure given the very small range that they were operating at. This caused fires to begin in the upper works with a fire consuming the entire center of the ship by the time that the Blucher had mostly made its way past the Norwegian guns. It was at that moment that the German ship came into the sights of the torpedo battery. These torpedoes were in fixed tubes, and so the officer in charge of them, Anderssen had precisely one chance to fire them at the German ship before it was no longer within the kill zone. But just before 4:30 and with the ship on fire it was easy to see exactly where the ship was, although it was going slower than expected. Anderssen himself pressed the firing key when the range was only 500 meters. He would later say that “I had never thought I would fire my torpedoes in anger” but that did not stop him from using them in the moment. Two torpedoes were fired, and both would hit, with the crewmen of the Blucher later recalling that they felt and heard heavy explosions. The torpedoes had hit very close together near one of the port side boiler rooms, and even if the crew of the Blucher did not yet know it, it sealed the fate of the ship.

As the Blucher was getting hit by torpedoes, behind the German flagship the the Deustchland class cruiser Lutzow was now receiving its own fire from some of the Norwegian shore batteries. But after seeing what had happened to the Hipper after a few shells hit the Lutzow the captain of the ship decided that on that specific morning caution was the better part of valor and ordered a retreat. With the other German ships abandoning the move up the fjord, it left only the Blucher, which was in a very bad state. The fires continued to rage along the upper decks, and it was starting to set off ammunition explosions throughout the ship. While the naval ammunition was kept as safe deeper in the ship the Blucher was also carrying a large amount of ammunition and supplies for the men that it was supposed to put ashore in Oslo, and this ammunition, with just as much explosive power was far more exposed. To make the situation somehow even more confusing, at some point smoke canisters began to ignite, covering the ship in a thick artificial smoke to go along with the very real smoke that the fires were creating. During damage control efforts the anchor was dropped to try and keep the ship from running ashore and over the next several hours the ship would circle around its anchor as the tide and wind changed. But regardless of the exact positioning of the Blucher, it was just a matter of time before the out of control fires finally made their way to something even more explosive than the infantry ammunition, and at 5:30 that is exactly what happened. It was at that time that the fire reached one of the 10.5cm magazines, and the explosions deep in the ship would rupture the bulkheads around the boiler room and the seal on the fuel tanks. The fuel rapidly leaked out onto the sea and caught fire. Without any other options, the captain ordered the crew to begin to abandon ship, but the only way to deliver this message was man to man because all ship wide communications had already been destroyed. As the decision was made to abandon ship, work began on trying to slip the anchor chain so that the ship would drift closer to the shore before the men were in the water, but as the ship started to list this became impossible. What the list reached 45 degrees the order could no longer be delayed and the crew began to abandon ship. Then men jumped overboard and began swimming to shore, at least 300 meters distant, and while there would be many survivors hundreds of sailors and soldiers would die, the exact number seems to be uncertain due to German attempts to downplay the disaster during the war and their long occupation of Norway. But the numbers seen to range from around 350 to over 1,000. There were reports from Norwegian witnesses that the Germans sang Deutschland, Deutschland uber alles as the ship slipped under the waves. Back on the Lutzow the captain of the now lead German ship did not really know what had happened to Blucher, all that was known was that the cruiser had taken heavy fire from Norwegian guns, was burning, but had continued on.


The retreat of the Lutzow and the German ships caused a lull in the fighting around Oscarsborg but in many other areas around Oslo the fighting continued to expand. Back at Rauøy further out in the fjord the situation was very rapidly getting serious when reports reached the fort that German officers, previously landed from the sea, had been asking around for how to get to Rauøy on the mainland. Shortly after these reports arrived, information about a German landing near one of the fort’s batteries arrived and a hasty ground defense force was thrown together. Every available body on the island, including gun crews from the other guns and anti-aircraft units. Bringing together all of these men brought the number up to about a hundred, and while they had two machine guns they had no real ability to actually attack the German soldiers that had landed. And so all they could really do is create a perimeter around the German troops and prevent them from taking over more of the island. Then around 8AM orders arrived from the Outer Oslofjord Naval Defense District that all hostilities were to end and that all defenses were to cease firing. Hesitant to follow these orders out of concern that they were a German fabrication, the commander of Rauøy Major Enger worked on verifying the authenticity of the order, it was genuine and he orders all of the men under his command to cease firing. This would be the fate of many small Norwegian units over the course of April 9th, a general feeling that they had the local situation under control, but forced to surrender as the general situation completely collapsed around them. After the failure of the initial German advance past Oscarsborg, the Luftwaffe was called in to bomb the defenders of Oscarsborg. They would arrive at about 7:45AM to drop their bombs, with bombs being dropped over the next several hours, but not continuously. At midday the Lutzow moved in to do a bit of shore bombardment. All of this caused a large amount of smoke and dust, but was not really that effective against the defenses and their defenders. Even with the fort seeming to be damaged, Captain Thiele of the Lutzow was still very hesitant to give things another go, and instead moved his ships to the nearby Horten. When he arrived at Horten he found it already occupied by German troops and troops from the Naval Task Force were landed to reinforce them until more arrived from Oslo. At around this time the Norwegian Admiral Smith-Johannsen who had commanded the naval bases at Horten was brought on board the Lutzow and was asked to order Oscarsborg to surrender. Smith-Johannsen refused, with the reasoning that after he had surrendered Horten to the Germans he no longer had the authority. Back near Oscarsborg the next German move was to land troops on Drøbak, which was a Norwegian fort on the mainland near Oscarsborg. The commander of the garrison, Captan Enger, not to be confused with Major Enger from Rauøy, knew that the Germans were landing, but was hesitant to open fire without explicit orders from Oscarsborg which did not arrive. And so instead of preparing a resistance Enger left his bunker to open discussions with the German officer who appeared to be in charge of the situation, and a surrender was quickly agreed to. Back on Oscarsborg the situation was obviously deteriorating very quickly. Observers from Oscarsborg could clearly see the landings that had just taken place at Drøbak, and there were reports that the Germans were in control of Oslo, that the government had fled the capital, and that other attacks had been made by the Germans. After discussions with his other officers Eriksen, seeing no real point in further resistance, discussions were opened with the Germans. Eriksen was quite the negotiator, or at least was stubborn enough to get better terms that some other garrisons on the morning of the 9th. The agreement which was eventually reached, after several hours of negotiations and the German desire to just get past the fort, was that the enlisted men and civilians from the fort would be released as soon as possible, and the officers would simply stay at the fortress for the itme being. The Norwegian flag was also allowed to fly next to the German flag the next morning. It was on that morning, the 10th of April that the German ships, led by the Lutzow were finally able to pass through the area around Oscarsborg, reaching Oslo at 10:45 in the morning. The efforts of the forts in the fjord, led by the men at Oscarsborg had delayed the German naval force for around 30 hours. After the war Eriksen would have to sit through two different investigative committees into his actions, with the charges that he had acted without specific orders during the events of April 9th and 10th. Unfortunately he would die in 1958, before his actions would be be exonerated, followed by a statue of him being placed at Oscarsborg in 1995.

While the naval situation was working itself out, there were many other German operations occurring around Oslo, with one of them being an attack on the Fornebu airfield to the southwest of Oslo. Fornebu would be the third airfield that was seen as critical to the success of the German invasion, with Aalborg and Sola being the other two, both of which were covered in the last episode. At Fornebu the plan was much the same, with about 340 German paratroopers dropping on the airfield to clear it for a larger number of infantry to be landed from transport planes. While at Aalborg and Sola the plan was generally followed quite closely, at Fornebu things began to go off script when some of the paratrooper transports ran into clouds and fog on their flight in. This would cause the enter first wave of transports, and all of the paratroopers, to turn around and head back to base. There was just one problem, the second wave of transports, carrying the infantry, were already in the air and were on their way to land at the airport, and they would not receive the information that the paratroopers had turned back. Over Fornebu 8 Bf-110s were in position to provide air support for the paratroopers, but then none arrived. This was a serious problem for the German pilots because they were planning to land and refuel their aircraft after the paratroopers were in control, and after orbiting waiting for the paratroopers to arrive they did not have the fuel to make it back to Germany. Just as things were becoming very troubling, finally the German transport planes arrived, but they did not fly over the airfield to drop paratroopers but instead lined up with the runway to land. These were the first transports of the second wave, who just assumed that the airfield was already in German hands and were going to land. A fully loaded transport aircraft isn’t exactly the most nimble aircraft, but as soon as the first transport landed Norwegian machine guns opened up on it, causing the pilot to immediately go to max power to take off. At this point the pilots of the Bf-110s needed something to happen immediately, they were running on fumes and some of the pilots were having to shut down one of their engines to save fuel. And so a few of the Bf-110s just started landing, with the others trying to suppress the Norwegian machine guns. This then caused German transports that were still arriving to believe that the airfield was under German control and they landed. As soon as the first German transport successfully landed the defenders were in serious trouble, they could not stem the tide of the arrival of German troops, and were not numerous enough to launch any kind of counterattack. The commander of the defenders pulled his troops back, not seeing any other option. The three Bf-110s that were still capable of flight were then refueled from Norwegian fuel supplies which were helpfully left intact and provided further air support as more and more German troops landed. There were several German and Norwegian casualties, and 2 German aircraft were destroyed with 5 damaged, but overall the attack on Fornebu was a lucky break for the Germans. It could have been a real disaster, but some lucky breaks and a lack of hesitation from the officers and men involved resulted in another German success.

The German planes over Fornebu were far from the other Luftwaffe aircraft over Oslo on the morning of April 9th. At dawn 25 German bombers were flying over the capital, with 14 more arriving shortly thereafter, the purpose of these initial aircraft was more as intimidation rather than active bombing. They were trying to move the Norwegians toward surrender, instead of a long drawn out resistance. Some of them were then dispatched to various areas like Rauøy and Oscarsborg to actually do some bombing. However, while the German aircraft were flying over Oslo one of the remarkable things was how few German troops were actually in the capital. The plan had been for about 900 infantry to fly into Fornebu and for some of those troops to quickly move into Oslo proper to prepare the way for the naval landings. But then the ships that were supposed to be executing those landings did not appear, as they were held up by Oscarsborg. This meant that for the first day of the invasion there were only about a thousand German troops in the capital, and the numbers would not really begin to expand until the Lutzow and the German ships finally made it to Oslo on the morning of the 10th. This disrupted the German plans, and delayed the arrival of the command staff for the invasion simply because Oslo was not secure. Unfortunately for the Norwegian’s, they were having many problems of their own simply due to the speed of German actions and the widespread nature of the German attacks. Throughout the early morning hours of April 9th reports were flooding into Norwegian leaders, both political and military leaders, of German attacks seemingly everywhere. Stavanger, Sola, Trondheim, Oslo, and Bergen all experienced German attacks. Some would go very poorly for the Norwegians, like at Sola, while others would go remarkably well like at Stavanger and Bergen. At Bergen the German cruiser Königsberg would join the list of German ships that were surprised by the power of Norwegian coastal fortifications, causing enough damage that it could not sail back to Germany out of concern for its seaworthiness. It would later be attacked by British aircraft, and then abandoned by the Germans. But damaging a few German naval vessels was not going to be enough to stop the tide of the German invasion. Next episode will dig deeper into the Norwegian government’s response to the unfolding invasion as they tried to determine any viable path forward.